Gear Pump

ABSTRACT

A gear pump includes: a pump chamber formed in the housing; a gear disposed in the pump chamber; a side plate disposed between a wall of the pump chamber and the gear, and arranged to seal a side surface of the gear, the side plate including an annular receiving portion formed between the wall of the pump chamber and the side plate, the receiving portion having a bottom portion and a side wall portion; a seal member disposed in the receiving portion of the side plate, and arranged to liquid-tightly separate the low pressure chamber and the high pressure chamber of the pump chamber; a pressure introducing section arranged to introduce a pressure generated by the pump operation, to a space between the bottom portion of the receiving portion and the seal member, and thereby to separate the seal member away from the bottom portion of the receiving portion.

BACKGROUND OF THE INVENTION

This invention relates to a gear pump.

A patent document (Japanese Patent Application Publication No. 11-303767) discloses a conventional gear pump including a gear, a seal, and a side plate. In this gear pump, at a low pressure of the discharge pressure of the gear pump, a pressing force of the side plate to a gear decreases by decreasing a reaction force of the seal. With this, a frictional force between the side plate and the gear decreases. On the other hand, at a high pressure of the discharge pressure, the pressing force of the side plate to the gear increases by increasing the reaction force of the seal. With this, it is possible to prevent the pressure from discharging along a side surface of the gear.

SUMMARY OF THE INVENTION

However, in the above-described conventional gear pump, a pressure receiving area with respect to a bottom portion of a receiving groove receiving the seal varies in accordance with the deformation of the seal by the pressure variation. Consequently, the variation of the pressing force of the side plate to the gear is generated. Therefore, the variation of the performance of the pump is generated.

It is an object of the present invention to provide a gear pump devised to solve the above mentioned problem, and to attain a desired stable pump ability.

According to one aspect of the present invention, a gear pump comprises: a housing; a pump chamber formed in the housing, the pump chamber having a low pressure chamber and a high pressure chamber; a gear disposed in the pump chamber, and arranged to be driven by a motor to perform a pump operation; a side plate disposed between a wall of the pump chamber and the gear, and arranged to seal a side surface of the gear, the side plate including an annular receiving portion formed between the wall of the pump chamber and the side plate, the receiving portion having a bottom portion and a side wall portion; a seal member disposed in the receiving portion of the side plate, and arranged to liquid-tightly separate the low pressure chamber and the high pressure chamber of the pump chamber; a pressure introducing section arranged to introduce a pressure generated by the pump operation, to a space between the bottom portion of the receiving portion and the seal member, and thereby to separate the seal member away from the bottom portion of the receiving portion.

According to another aspect of the invention, a gear pump comprises: a housing; a pump chamber formed in the housing, the pump chamber having a high pressure chamber and a low pressure chamber; a gear disposed within the pump chamber, and arranged to rotate at least by a drive shaft; a side plate disposed adjacent to the gear, between a side surface of the gear and a wall of the pump chamber, the side plate having an annular recessed groove formed in a surface confronting the wall of the pump chamber, and the annular recessed groove having a bottom portion; and a seal member disposed in the annular recessed groove of the side plate, and arranged to separate the high pressure chamber and the low pressure chamber of the pump chamber, and to be pushed in a direction away from the bottom portion of the recessed groove by a pressure introduced from the high pressure chamber when the gear is driven.

According to still another aspect of the invention, a gear pump comprises: at least a pair of gears engaged with each other; a side plate disposed adjacent to the gears, the side plate including an annular recessed groove, and a shoulder portion; a housing disposed at a position to sandwich the side plate with the gear, and to confront the gear; a seal member disposed in the annular recessed groove of the side plate, and arranged to seal a gap between the housing and an end of the shoulder portion of the side plate, and to separate a low pressure chamber and a high pressure chamber formed in a radial direction of the gear; and a pressure introducing section arranged to transform the seal member by a pressure of the high pressure chamber in a direction toward the end of the shoulder portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a rear perspective view showing a gear pump according to a first embodiment of the present invention.

FIG. 2 is a front view showing the gear pump of FIG. 1.

FIG. 3 is an enlarged view showing a main part of the gear pump of FIG. 1.

FIG. 4 is an enlarged view showing a main part of the gear pump of FIG. 1.

FIG. 5 is a front perspective view showing a seal member of the gear pump of FIG. 1.

FIG. 6 is a rear perspective view showing the seal member of the gear pump of FIG. 1.

FIG. 7 is a front perspective view showing a first side plate of the gear pump of FIG. 1.

FIG. 8 is a front perspective view showing the first side plate of the gear pump of FIG. 1.

FIG. 9 is a front view showing the first side plate of the gear pump of FIG. 1.

FIG. 10 is a rear view showing the first side plate of the gear pump of FIG. 1.

FIG. 11 is a top view showing the first side plate of the gear pump of FIG. 1.

FIG. 12A is a view illustrating a state before the gear pump of FIG. 1 is connected with a motor. FIG. 12B is a view illustrating a state after the gear pump of FIG. 1 is connected with the motor.

FIG. 13 is a view illustrating an arrangement of the first side plate and the first gear of the gear pump of FIG. 1.

FIG. 14 is a view illustrating an arrangement of the seal member, the first side plate and the first gear of the gear pump of FIG. 1.

FIG. 15 is a sectional view taken along a section line A15-A15 of FIG. 14.

FIG. 16 is a rear perspective view showing the first side plate and the seal of the gear pump of FIG. 1.

FIG. 17 is a partially sectional perspective view taken along a section line of A17-A17 of FIG. 16.

FIG. 18A is a view illustrating a state in which the gear pump is mounted. FIG. 18B is a view illustrating a state in which a low pressure is acted to the seal. FIG. 18C is a view illustrating a state in which a high pressure is acted to the seal.

FIGS. 19A to 19C are views illustrating a general seal of a conventional gear pump apparatus. FIG. 19A is a view illustrating a state in which seal S5 is mounted. FIG. 19B is a view illustrating a state in which a low pressure is acted to the seal. FIG. 19C is a view illustrating a state in which a high pressure is acted to the seal.

FIG. 20 is a view illustrating a brake apparatus to which the gear pump of FIG. 1 is attached.

FIG. 21A is a view illustrating a state in which the seal is mounted in a gear pump according to a second embodiment of the present invention. FIG. 21B is a view illustrating a state in which a low pressure is acted to the seal. FIG. 21C is a view illustrating a state in which a high pressure is acted to the seal.

FIGS. 22A, 22B and 22C are views showing the gear pump according to the second embodiment when the high pressure side and the low pressure side are reversed. FIG. 22A is a view illustrating a state in which the seal is mounted. FIG. 22B is a view illustrating a state in which a low pressure is acted to the seal. FIG. 22C is a view illustrating a state in which a high pressure is acted to the seal.

FIG. 23 is a sectional view illustrating a gear pump according to a third embodiment of the present invention.

FIG. 24 is a view showing a seal of a gear pump according to a fourth embodiment of the present invention.

FIG. 25 is a sectional view illustrating a gear pump according to a fifth embodiment of the present invention.

FIG. 26 is a sectional view illustrating a first gear and a second gear of the gear pump of FIG. 25.

FIG. 27 is an enlarged sectional view showing a portion of a first side plate near a seal in the gear pump of FIG. 25.

FIG. 28 is an enlarged sectional view showing a portion of a second side plate near a seal in the gear pump of FIG. 25.

FIGS. 29A, 29B and 29C are enlarged sectional views showing a portion near a seal of a gear pump according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, gear pumps according to embodiments of the present invention are illustrated.

First Embodiment

Hereinafter, a gear pump according to a first embodiment of the present invention is illustrated. FIG. 1 is a rear perspective view showing the gear pump according to a first embodiment of the present invention. FIG. 2 is a front view showing the gear pump 1 of FIG. 1. As shown in FIGS. 1 and 2, gear pump 1 is used as an actuator for controlling a brake fluid pressure of a vehicle. Gear pump 1 includes a housing 2, and a pump assembly 3 received in housing 2.

[Housing] Next, housing 2 is illustrated. Housing 2 is formed into a substantially rectangular shape. Housing 2 includes a plurality of mounting holes 2 a which are formed on an outer surface of housing 2, and to which selector valves (not shown) and sensors (not shown) are mounted. Gear pump 1 includes a pump chamber 4 which is formed on a front surface of housing 2 at a substantially central position of housing 2, which is recessed into a substantially cylindrical shape, which has a stepped cylindrical shape having different diameters, and which receives pump assembly 3.

[Pump Assembly] Next, pump assembly 3 is illustrated. A side of an open end of pump chamber 4 (side of a second pump 9 described later) represents a front side (lower side of FIG. 3). A side of a bottom of pump chamber 4 (side of a first pump 8 described later) is a rear side (upper side of FIG. 3). As shown in FIGS. 3 and 4, pump assembly 3 includes a plug member 5, a cover member 6, a seal member 7, a first pump 8, a second pump 9 and so on. Plug member 5 is shaped like a circular disc. Plug member 5 includes a through hole 5 a which is located at a substantially central position of plug member 5, and which is a hexagonal through hole penetrating through plug member 5. Moreover, plug member 5 includes a rear surface 5 d which is located at a rear end portion of plug member 5, and which is abutted on cover member 6; and an annular protrusion 5 b which surrounds an outer circumference of rear surface 5 d, and which protrudes in the rearward direction. Moreover, plug member 5 includes an externally threaded portion 5 c formed on an outer circumference surface of plug member 5. Externally threaded portion 5 c of plug member 5 is screwed into an internally threaded portion 4 a formed on an inner circumference surface of pump chamber 4. Cover member 6 is shaped like a circular disc. Cover member 6 includes a front surface 6 e abutted on plug member 5, and a stepped portion 6 f cut around an outer circumference surface of front surface 6 e. Front surface 6 e is pushed rearwards by an axial force produced by plug member 5 when plug member 5 is screwed into pump chamber 4, and consequently front surface 6 e is abutted on rear surface 5 d of plug member 5. Plug member 5 is disposed at a predetermined position in a state in which annular protrusion 5 b of plug member 5 is fit on stepped portion 6 f of cover member 6. Cover member 6 includes a raised portion 6 g which is formed on the outer circumference surface of cover member 6, which has an outside diameter substantially identical to an inside diameter of pump chamber 4, and an outside diameter of annular protrusion 5 b of plug member 5. Moreover, cover member 6 includes a seal groove 6 h formed on the outer circumference surface of cover member 6, and located on a rear side of raised portion 6 g. An annular seal S1 is disposed between raised portion 6 g of cover member 6 and annular protrusion 5 b of plug member 5 to seal a clearance radially between the outside surface of cover member 6 and the inside surface of pump chamber 4. An annular seal S2 is provided in seal groove 6 h to seal a clearance between cover member 6 and the inner circumference of pump chamber 4. That is, seals S1 and S2 are mounted, respectively, at positions away from each other in the forward and rearward directions (in the upward and downward directions). Cover member 6 includes a stepped through hole 6 b which is located in an eccentric position of cover member 6. Stepped through hole 6 b includes a larger diameter (front) portion and a smaller diameter (rear) portion having an inside diameter smaller than the inside diameter of the larger diameter portion. A drive shaft 10 is inserted in this stepped through hole 6 b with a clearance 6 a in the smaller diameter portion. Annular seals S3 are disposed, respectively, in the larger diameter portion and the smaller diameter portion of stepped through hole 6 b to seal a clearance around drive shaft 10. Moreover, cover member 6 includes an annular recessed portion 6 d located at a rear end portion of cover member 6, and recessed in the forward direction; and an annular protrusion 6 c protruding from recessed portion 6 d in the rearward direction. On an inner circumference surface of annular protrusion 6 c, there is formed a stepped portion 6 i which is cut around the inner circumference surface of annular protrusion 6 c.

As shown in FIGS. 5 and 6, seal member 7 is formed into a substantially circular disc shape. Seal member 7 includes a pair of through holes 7 a and 7 b which are apart from each other in the upward and downward directions, each of which has a circular opening, and each of which penetrates in the forward and rearward directions. Moreover, seal member 7 includes side seal portions 7 d which are formed, respectively, on the front and rear surfaces of seal member 7, each of which surround through holes 7 a and 7 b, and each of which protrudes in the axial direction. Each of side seal portions 7 d includes a pair of engagement raised portions 7 e each protruding from the side seal portion 7 d in the lateral direction. Each of side seal portions 7 d includes an annular ring receiving portion 7 f which has a center identical to the center of through hole 7 a, and which is recessed in the inward direction of the thickness (axially inwards). Seal member 7 includes an annular seal receiving groove 7 g which is recessed in the inside direction of the thickness in ring receiving portion 7 f on the rear surface of seal member 7, which has a smaller diameter, and which is continuous with ring receiving portion 7 f. Moreover, seal member 7 includes an annular receiving portion 7 h formed on the outer circumference surface of seal member 7, and recessed radially inwards; and an annular protrusion 7 i which is located in a front end portion of seal member 7, and which protrudes in the forward direction.

As shown in FIGS. 3 and 4, seal member 7 is pushed in the rearward direction through cover member 6 by the axial force produced by plug member 5 when screwed into pump chamber 4. Consequently, annular protrusion 7 i of seal member 7 is mounted in (fit in) stepped portion 6 i of cover member 6. An outer region of the rear side surface of seal member 7 abuts on stepped portion 4 b of pump chamber 4, so that seal member 7 is reliably positioned at a predetermined position. Drive shaft 10 is inserted into through hole 7 a of seal member 7. A driven shaft 11 is inserted into through hole 7 b of seal member 7. An annular rotation seal member (X-ring and so on) 12 is mounted in seal receiving portion 7 g of seal member 7 to seal between the drive shaft 10 and a first pump chamber P1 described later. Moreover, a first annular seal ring 13 a is mounted in ring receiving portion 7 f on the rear side surface of seal member 7 to close seal receiving portion 7 g of rotation seal member 12. A second annular seal ring 13 b is mounted in ring receiving portion 7 f on the front side surface of seal member 7. Each of seal rings 13 a and 13 b is made of a material which is more rigid and more durable than a material of seal member 7. Moreover, an annular seal S4 is mounted in receiving portion 7 h of seal member 7. Annular seal S4 contacts the inner circumference surface of pump chamber to seal between first pump chamber P1 and second pump chamber P2. First pump chamber P1 is formed between seal member 7 and an annular recessed portion 4 c recessed in the rearward direction from stepped portion 4 b of pump chamber 4. First pump chamber P1 is a closed space. First pump 8 is disposed in first pump chamber P1. On the other hand, a second pump chamber P2 is formed between seal member 7 and a recessed portion 6 d of cover member 6. Second pump chamber P2 is a closed space. Second pump 9 is disposed in second pump chamber P2. First pump 8 is provided with (includes) a first gear 15 having a front surface, a rear surface, and tooth top portions which are sealed by seal member 7 and first side plate 14 described later.

Next, first side plate 14 is illustrated. As shown in FIGS. 7-11, first side plate 14 is formed into a substantially triangular shape, as viewed from the forward direction. First side plate 14 is made of a resin. First side plate 14 includes three through holes 14 a, 14 b and 14 c which are formed, respectively, near apexes of the triangular shape of first side plate 14, and which penetrate through first side plate 14. First side plate 14 includes a side seal portion 14 d which is located around through holes 14 a and 14 b on the front surface of first side plate 14, and which protrudes in the forward direction. First side plate 14 includes a seal block 14 e which is shaped like a triangular shape, which is formed on the front surface of first side plate 14, and which protrudes in the forward direction. Seal block 14 e of first side plate 14 includes a passage portion 14 f forming an open portion extending continuously from the through hole 14 c toward the center of first side plate 14; a pair of tooth top seal portions 14 g which are formed on both sides of the passage section 14 f, which are continuous with a part of the side seal portion 14 d, and which are in the form of a curved surface; and engagement portions 14 h located on the front side of the respective tooth top seal portions 14 g. Moreover, seal block 14 e includes a groove 14 i which is recessed in the inward direction of the thickness, and which surrounds through hole 14 c from the outer circumference of tooth top seal portions 14 g. On the other hand, first side plate 14 includes a receiving portion 14 j which is formed on the rear surface of first side plate 14, which has three circular portions having different diameters, and which surround through holes 14 a, 14 b and 14 c, as shown in FIG. 10.

As shown in FIG. 4, drive shaft 10 is rotatably inserted into through hole 14 a of first side plate 14 with a radial clearance. On the other hand, driven shaft 11 is inserted into through hole 14 b of first side plate 14 with a radial clearance. Moreover, a seal S5 described later is fit in receiving portion 14 j to seal between the high pressure side and the low pressure side of first pump chamber P1, as described later.

Next, first gear 15 is illustrated. As shown in FIGS. 13 and 14, first gear 15 includes a drive gear 16 into which driver shaft 10 is inserted; and a driven gear 17 into which driven shaft 11 is inserted. A tooth top 16 a of drive gear 16 and a tooth top 17 a of driven gear 17 are engaged with each other at a tooth engagement portion (region) 18. Drive shaft 10 includes a recessed portion 10 a located in a position corresponding to drive gear 16, and recessed radially inwards. A cylindrical drive pin 10 b is received in this recessed portion 10 a. Drive pin 10 a extends from a center of drive shaft 10 in the radial direction. Drive pin 10 b includes a first end received in recessed portion 10 a of drive shaft 10, and a second end engaged with a recessed portion 16 b which is recessed radially inward from the inner circumference surface of drive gear 16. On the other hand, drive shaft 11 includes a recessed portion 11 a located in a position corresponding to driven gear 17, and recessed radially inwards. A cylindrical driven pin 11 b is received in this recessed portion 11 a. Driven pin 11 b extends from a center of driven shaft 11 in the radial direction. Driven pin 11 b includes a first end received in recessed portion 11 a of driven shaft 11, and a second end engaged with a recessed portion 17 b which is recessed radially outwards from the inner circumference surface of driven gear 17.

Moreover, drive shaft 10 includes a mounting raised portion 19 which has a substantially rectangular column, and which is located at a front end portion of drive shaft 10, as shown in FIGS. 12A and 12B. A rotational shaft 20 a of motor M1 includes a mounting recessed portion 20 b which is located at an end portion of rotational shaft 20 a, and which is arranged to be engaged and connected with mounting raised portion 19 of drive shaft 10. Accordingly, motor M1 drives and rotates drive shaft 10 around rotational shaft 20 a. Moreover, drive pin 10 b is engaged with drive gear 16, and arranged to prevent the rotation of drive gear 16 relative to drive shaft 10, and to cause the drive gear 16 to rotate as a unit with drive shaft 10. When drive shaft 10 is driven, drive gear 16 rotates in accordance with the rotation of drive gear 16 in the same direction as drive shaft 10. On the other hand, drive gear 17 is engaged with drive gear 16. Driven pin 11 b is engaged with driven gear 17, and to prevent the rotation of drive gear 17 relative to driven shaft 11. Accordingly, driven gear 17 rotates together with driven shaft 11 in a direction opposite to the rotational direction of drive shaft 10.

As shown in FIG. 13, tooth tops 16 a and 17 a of gears 16 and 17 are liquid-tightly and slidably abutted, respectively, on tooth top seal portions 14 g of seal block 14 e of first side plate 14. As shown in FIGS. 14 and 15, the pair of engagement raised portions 7 e on the rear surface of seal member 7 are engaged with and contacted on, respectively, the curved surfaces of the engagement portions 14 h of seal block 14 e, so as to seal tooth tops 16 a and 17 a of gears 16 and 17 with side seal portion 14 d of first side plate 14. A substantially triangular holding member 21 is mounted around the corresponding side seal portion 7 d of seal member 7 and groove 14 i formed in the outer circumference of seal block 14 e (cf. FIG. 14). In pump chamber 4, there are provided a suction port (not shown) connected with through hole 14 c of first side plate 14 and a discharge port (not shown) connected with first pump chamber P1. On the other hand, second pump 9 is symmetrical to first pump 8 with respect to seal member 7. That is, there is provided a second gear 23 having front and rear surfaces sealed by seal member 7 and second side plate 22. Second side plate 22 and second gear 23 are bilaterally symmetrical to first side plate 14 and first gear 15. Therefore, the illustration is omitted.

As shown in FIG. 4, drive shaft 10 is rotatably inserted into through hole 22 a of second side plate 22 with a radial clearance. On the other hand, driven shaft 11 is inserted into through hole 22 b of second side plate 22 with a radial clearance. Second side plate 22 includes a receiving portion 22 j which is identical in shape to receiving portion 14 j of first side plate 14. A seal S6 identical in shape to seal S5 is fit in receiving portion 22 j of second side plate 22 to seal between the high pressure side and the low pressure side of second pump chamber P2 as described later.

In second pump 9, pump chamber 4 includes a suction port (not shown) connected through a through hole 22 c of second side plate 22 and a hydraulic passage of cover member 6; and a discharge port (not shown) connected with second pump chamber P2 through a hydraulic passage formed in cover member 6, unlike first pump 8. The other structures of second pump 9 is substantially identical to the structure of first pump 8. Each of through holes 14 a and 22 a of side plates 14 and 22 has a diameter larger than a diameter of drive shaft 10. Each of through holes 14 b and 22 b has a diameter larger than a diameter of driven shaft 11. That is, drive shaft 10 is inserted into through holes 14 a and 22 a of first and second side plates 14 and 22 with slight radial clearances, and driven shaft 11 is inserted into through holes 14 b and 22 b of first and second side plates 14 and 22 with slight radial clearances.

[Receiving Portion] Next, receiving portions 14 j and 22 j of first and second side plates 14 and 22 are illustrated. Receiving portion 22 j is identical in shape to receiving portion 14 j. Therefore, only receiving portion 14 j is illustrated. Receiving portion 14 j is recessed on the rear surface of first side plate 14, as shown in FIGS. 16 and 17. Receiving portion 14 j includes a bottom portion 30 extending in a direction perpendicular to the axial direction of first side plate 14; a high pressure side wall portion 31 which extends continuously with bottom portion 30, and which is inclined; and a low pressure side wall portion 32 extending in a direction perpendicular to bottom portion 30. Receiving portion 14 j has a substantially V-shaped cross section. Receiving portion 14 j includes a plurality of communicating grooves 33 (five communicating groove in the first embodiment) each formed on high pressure side wall portion 31, by cutting high pressure side wall portion 31 to increase the width of bottom portion 30 toward high pressure side wall portion 31. Communicating grooves 33 receive seal S5 which is a transformed annular shape bent in a substantially triangular shape, which has a circular cross section, and which is made of an elastic material such as rubber. In particular, as shown in FIG. 18A, seal S5 is disposed with a clearance or void 34 between seal S5 and bottom portion 30. Seal S5 abuts on high pressure side wall portion 31 and low pressure side wall portion 32 of receiving portion 14 j, and recessed portion 4 c.

Next, operation of the first embodiment is illustrated. [Assembly Operation of Gear Pump] Next, assembly operation of gear pump 1 is illustrated. In the assembly operation of this gear pump 1, rotation seal member 12 is inserted into and temporally fixed to seal receiving portion 7 g of seal member 7 preliminary equipped with seal S4. Then, drive shaft 10 is inserted into through hole 7 a of seal member 7, and driven shaft 11 is inserted into through hole 7 b of seal member 7. Next, seal rings 13 a and 13 b are inserted, respectively, into ring receiving portions 7 f. In this case, rotation seal member 12 is pushed by first ring 13 a, so that rotation seal member 12 appropriately contacts drive shaft 10. Then, drive pins 10 b and 10 e and driven pins 11 b and 11 d are inserted, respectively, into recessed portions 10 a and 10 d of drive shaft 10 and recessed portions 11 a and 11 c of driven shaft 11. Next, drive gears 16 and 26 and driven gears 17 and 27 are assembled, respectively, into drive shaft 10 and driven shaft 11. Then, drive shaft 10 and driven shaft 11 are inserted, respectively, into first and second side plates 14 and 22 preliminary equipped with seals S5 and S6 and holding members 21 and 24, and so that first and second side plates 14 and 22 are assembled to seal member 7. In this case, on first side plate 14's side of seal member 7, the pair of engagement portions 7 e of seal member 7 are engaged, respectively, with the engagement portions 14 h of first side plate 14 to position seal member 7 and first side plate 14. Therefore, it is facilitate the assembly operation by positioning seal member 7 and first side plate 14. Holding member 19 can temporarily hold and fix seal member 7 and first side plate 14. Holding member 16 can be readily mounted on seal member 7 and first side plate 14 by first mounting the holding member 16 on seal member 7, and then expanding holding member 16 onto first side plate 14. Similarly, on the second side plate 22's side, the pair of engagement raised portions 7 e of seal member 7 are engaged, respectively, with the engagement portions of second side plate 22 to position seal member 7 and second side plate 22. Therefore, it is facilitate the assembly operation by positioning seal member 7 and second side plate 22. Holding member 24 can be readily mounted on seal member 7 and first side plate 14 by first mounting the holding member 24 on seal member 7, and then expanding holding member 24 onto second side plate 22. Next, drive shaft 10 is inserted into through hole 6 a of cover member 6 provisionally equipped with seals S1 and S2. Annular protrusion 6 c of cover member 6 is mounted on seal member 7 to assemble cover member 6 and seal member 7, so that pump assembly 3 is assembled.

Next, the thus-assembled pump assembly 3 is inserted into pump chamber 4 of housing 2. Then, plug member 5 is screwed into and fixed to pump chamber 4. In this case, seal member 7 can be stably contacted with and fixed to stepped portion 4 b of pump chamber 4 by the axial force produced by plug member 5 when plug member 5 is screwed into pump chamber 4. Accordingly, it is possible to dispose each member in an accurate position in the forward and rearward directions, and to prevent the unsteadiness or shakiness by the pressure variation of the hydraulic fluid described later. In addition, seal S1 is pushed by annular protrusion 5 b of plug member 5, and accordingly it is possible to improve the seal ability between pump chamber 4 and cover member 6. In this way, in gear pump 1 according to the first embodiment, pump assembly 3 can be received in housing 2 in the temporally assembled state of pump assembly 3. Accordingly, it is possible to simplify the assembly operation.

[Operation of Gear Pump] Next, the operation of gear pump 1 is illustrated. The thus-constructed gear pump 1 is provided at the end portion of the cylindrical drive shaft 10, as shown in FIGS. 12A and 12B. Mounting raised portion 19 of gear pump 1 is connected with mounting recessed portion 20 b of rotational shaft 20 a of motor M1.

When drive shaft 10 is rotated by motor M1 in a direction shown by an arrow of FIG. 13, driven gear 17 of first pump 8 is driven through drive gear 16. By this operation, the hydraulic fluid of the low pressure is introduced from through hole 14 c of seal block 14 e of first side plate 14 which is connected with the suction port, and the hydraulic fluid of the high pressure is outputted to pump chamber P1. This hydraulic fluid of the high pressure is outputted to the corresponding discharge port. Similarly, in second pump 9, driven gear 27 is driven through drive gear 26, like first gear pump 8. By this operation, the hydraulic fluid of the low (negative) pressure is introduced from through hole 22 c of seal block 22 e of second side plate 22, and the high pressure hydraulic fluid is outputted to pump chamber P2. This hydraulic fluid of the high pressure is outputted to the corresponding discharge port. In this way, gear pump 1 can perform the suction operations and the discharge operations of the hydraulic fluid in the pump chambers P1 and P2 in the two separate piping systems. That is, gear pump 1 serves as a tandem external gear pump.

[Pressing Force of Side Plate to Gear] Next, the pressing forces of first and second side plates 14 and 22 to gears 15 and 23 are illustrated. The pressing force by first side plate 14 to gear 15 is identical to the pressing force by second side plate 22 to gear 23. Therefore, the only pressing force by first side plate 14 to gear 15 is illustrated. FIG. 18A is a view illustrating a state in which seal S5 is mounted. FIG. 18B is a view illustrating a state in which a low pressure is acted to seal S5. FIG. 18C is a view illustrating a state in which a high pressure is acted to seal S5. As described above with reference to FIG. 18A, seal S5 is disposed with the clearance between bottom portion 30 of receiving portion 14 j and seal S5, and seal S5 abuts on high pressure side wall portion 31, low pressure side wall portion 32, and recessed portion 4 c. Accordingly, seal S5 is disposed in the clearance between first side plate 14 and recessed portion 4 c to separate the high pressure chamber H1 and the low pressure chamber L1. At the low pressure operation of the hydraulic fluid by the actuation of first pump 8, seal S5 is transformed (varies its shape) by receiving the pressure of the hydraulic fluid from the high pressure chamber H1, and transformed (varies its shape) toward low pressure chamber L1 (the diameter of seal S5 decreases), as shown in FIG. 18B. Seal S5 seals and divides between the high pressure chamber H1 and the low pressure chamber L1. The hydraulic fluid of the high pressure chamber H1 is introduced through communicating groove 33 to clearance 34 in response to the transformation of seal S5. High pressure side wall portion 31 includes a holding portion 35 to dispose and hold seal S5 in a predetermined position. Communicating groove 33 has a width W1 larger than a width W2 of holding portion 35 with respect to bottom portion 30. Therefore, the hydraulic fluid can be introduced from communicating groove 33 to clearance 34. Next, at the high pressure operation of the hydraulic fluid by the actuation of first pump 8, seal S5 is moved away from bottom portion 30 by the pressure of the hydraulic fluid flowing into clearance 34, as shown in FIG. 18C. Seal S5 surely seals between the high pressure side H1 and the low pressure side L1. In this case, seal S5 can be away from bottom portion 30, and completely floated from bottom portion 30.

FIGS. 19A to 19C are views illustrating a general seal of a conventional gear pump apparatus. FIG. 19A is a view illustrating a state in which seal S5 is mounted. FIG. 19B is a view illustrating a state in which a low pressure is acted to the seal. FIG. 19C is a view illustrating a state in which a high pressure is acted to the seal. In the general gear pump as shown in FIGS. 19A-19C, the pressing force to the gear is calculated by a following mathematical expression (1).

The pressing force to the gear=(the pressure receiving area of the side plate on the receiving portion's side−the pressure receiving area of the side plate on the gear's side)×the pressure in the pump chamber+the seal reaction force  (1)

In case of the gear pump described in Patent Document 1 employing a general receiving portion of a recessed shape as shown in FIGS. 19A-19C, the pressure receiving area α (FIGS. 19-19C) of the side plate on the receiving portion's side is varied in accordance with the transformation of the seal by the pressure variation. Moreover, the reaction force of the seal varies in accordance with the pressure variation. Accordingly, the seal reaction force is not stable. In FIGS. 19A-19C, the same reference numerals are given to similar component parts. Moreover, in general, the seal is made of a rubber. Accordingly, the curing and the wear-out are generated due to the long time use, so that the variation of the reaction force is large. Moreover, it is not possible to neglect the variation of the reaction force by the dimension variation since it is not possible to decrease the manufacturing dimension tolerance, and the assembly dimension tolerance of the rubber. Accordingly, in fact, it is difficult eliminate the variation of the pressing force of the side plate to the gear. This variation of the pressing force adversely affects the pumping performance. On the other hand, in the first embodiment, at the low to high pressure operation in which the pressure is applied to the hydraulic fluid, the entire of the receiving portion 14 j to low pressure side wall portion 32 is the pressure receiving area a of side plate 14 on the receiving portion's side (cf. FIGS. 18B and 18C). Moreover, at the operation of the high pressure of the hydraulic fluid, seal S5 is away from bottom portion 30, and completely floated away from bottom portion 30, so that the reaction force of seal S5 is eliminated. Accordingly, the pressing force to gear 15 in gear pump 1 of the first embodiment is calculated by a following mathematical expression (2).

The pressing force to gear 15=(the pressure receiving area of first side plate 14 on the receiving portion 14j's side (constant)−the pressure receiving area of first side plate 14 on the gear 15's side (constant))×the pressure in the first pump chamber P1  (2)

Accordingly, first gear 15 receives little influence from the transformation of seal S5 and the reaction force of seal S5 by the pressure variation in first pump P1. Therefore, even when the pressure increases in first pump P1, it is possible to decrease the pressing force by the elimination of the reaction force of seal S5. Moreover, it is possible to decrease the friction between first side plate 14 and gear 15 by decreasing the pressing force, and to improve the pump ability (performance). Moreover, even when seal S5 is transformed (varies its shape), the pressure receiving area of first side plate 14 on the receiving portion 14 j's side is held constant. Accordingly, it is possible to exclude the dimension variation of seal S5, and to readily set an appropriate valance shape of first side plate 14. Moreover, the factor of the variation of the pressing force becomes only the inner pressure inside first pump chamber P1. Accordingly, it is possible to decrease the variation, and to ensure the stable pump performance. In gear pump 1 according to the first embodiment, seal S5 is completely floated from bottom portion 30 at the high pressure operation of the hydraulic fluid. Moreover, seal S5 may be arranged to be floated from bottom portion 30 at the low pressure operation of the hydraulic fluid.

[Molding of Receiving Portion] In the first embodiment, each of side plates 14 and 22 is made of resin, and integrally molded. Accordingly, it is possible to readily mold each portion of receiving portions 14 j and 22 j. Moreover, it is possible to readily form communicating groove 33 by varying a part of the width of bottom portion 30.

[Stability of Friction] In the first embodiment, clearance 34 is formed in advance between each of seals S5 and S6 and the corresponding bottom portion 30. The pressure is supplied to clearance 34. Accordingly, it is possible to improve the responsiveness to the supply of the hydraulic fluid. Therefore, it is possible to rapidly stabilize the friction suddenly after the start of the operation of each of pumps 8 and 9.

[Application to Brake Apparatus] Next, application of gear pump 1 to a brake apparatus for a vehicle is illustrated. A structure of the brake apparatus described below is one example. Gear pump 1 can be applicable to other known brake apparatuses, and applicable to other apparatuses other than the brake apparatus.

As shown in FIG. 20, a brake apparatus 101 according to the first embodiment has an X-piping system having a P-system and an S-system. A booster Bs and so on are identical in a structure to a booster and so on of the conventional apparatus. Therefore, the different parts are illustrated below. The P-system is connected with a wheel cylinder W/C (FL) of a front left wheel and a wheel cylinder W/C (RR) of a rear right wheel. The S-system is connected with a wheel cylinder W/C (FR) of a front right wheel and a wheel cylinder W/C (RL) of a rear left wheel. The P-system and the S-system are connected, respectively, with pump 8 and pump 9 of gear pump 1. Master cylinder M/C is connected with the suction sides of pumps 8 and 9 by passages 11P and 11S. Reservoirs 160P and 160S are disposed, respectively, in passages 11P and 11S. Each of reservoirs 160P and 160S has a check valve function. Reservoirs 160P and 160S have the same functions, and therefore only reservoir 160P is illustrated. Reservoir 160P includes a ball valve 161; a piston 162; a spring 163 arranged to urge piston 162 in the upward direction; a port 164 arranged to introduce, to reservoir 160P, a brake fluid flowing from the wheel cylinder by the pressure reduction; a port 165 arranged to introduce, to the pump suction side, a brake fluid within reservoir 160P or the brake fluid in the master cylinder. When the master cylinder pressure is generated, ball valve 161 is closed. When pump 8 is actuated in this state, ball valve 161 is opened by the difference between the pressure receiving areas of ball valve 161 and piston 162, and the spring elastic force. The brake fluid is appropriately sucked.

A master cylinder pressure sensor PMC is provided between master cylinder M/C and reservoir 160P, and arranged to sense a pressure of master cylinder M/C. A check valve 6P is provided in passage 11P between reservoir 160P and pump 8, and arranged to allow a flow of the brake fluid from reservoir 160P to pump 8, and to restrict a flow of the brake fluid from pump 8 to reservoir 160P. A check valve 6S is provided in passage 11S between reservoir 160S and pump 9, and arranged to allow a flow of the brake fluid from reservoir 160S to pump 9, and to restrict a flow of the brake fluid from pump 8 to reservoir 160S. The discharge sides of pumps 8 and 9 are connected, respectively, with the wheel cylinders by passages 12P and 12S. In passages 12P and 12S, there are provided solenoid-in-valves 4FL, 4RR, 4FR and 4RL each of which is a normally-open solenoid valve. A check valve 7P is provided in passage 12P between pump 8 and solenoid-in-valves 4FL and 4RR, and arranged to allow flows of the brake fluid from pump 8 to solenoid-in-valves 4FL and 4RR, and to restrict flows of the brake fluid from solenoid-in-valves 4FL and 4RR to pump 8. A check valve 7S is provided in passage 12S between pump 9 and solenoid-in-valves 4FR and 4RL, and arranged to allow flows of the brake fluid from pump 9 to solenoid-in-valves 4FR and 4RL, and to restrict flows of the brake fluid from solenoid-in-valves 4FR and 4RL to pump 9. Moreover, in passages 12P and 12S, there are provided, respectively, passages 17FL and 17RR, and passages 17FR and 17RL to divert (bypass) solenoid-in-valves 4FL, 4RR, 4FR and 4RL. In passages 17FL, 17RR, 17FR and 17RL, there are provided, respectively, check valves 10FL, 10RR, 10FR and 10RL. These check valves 10FL, 10RR, 10FR and 10RL are arranged to allow, respectively, flows of the brake fluid from wheel cylinders W/C to pumps 8 and 9, and to restrict, respectively, flows of the brake fluid from pumps 8 and 9 to wheel cylinders W/C. Master cylinder M/C is connected, respectively, with passages 12P and 12S by passages 13P and 13S. Passage 12P and passage 13P are connected (joined) between pump 8 and solenoid-in-valve 4FL and 4RR. Passage 12S and passage 13S are connected (joined) between pump 9 and solenoid-in-valve 4FR and 4RL. In passages 13P and 13S, there are provided, respectively, gate out valves 3P and 3S each of which is a normally open solenoid valve. Each of passages 13P and 13S includes a master side passage 13 a which is located between master cylinder M/C and the corresponding gate out valve 3P and 3S; and a wheel side passage 13 b which is located between the wheel cylinders and the corresponding gate out valve 3P and 3S. In passages 13P and 13S, there are provided, respectively, passages 18P and 18S to divert (bypass) gate out valves 3P and 3S. A check valve 9P is provided in passage 18P, and arranged to allow a flow of the brake fluid from master cylinder M/C to wheel cylinders W/C, and to restrict a flow of the brake fluid from wheel cylinders W/C to master cylinder M/C. A check valve 9S is provided in passage 18S, and arranged to allow a flow of the brake fluid from master cylinder M/C to wheel cylinders W/C, and to restrict a flow of the brake fluid from wheel cylinders W/C to master cylinder M/C.

On the suction sides of pumps 8 and 9, there are provided reservoirs 160P and 160S. Reservoirs 160P and 160S are connected, respectively, with pumps 8 and 9 by passages 15P and 15S. A check valve 6P is provided between reservoir 160P and pump 8, and arranged to allow a flow of the brake fluid from reservoir 160P to pump 8, and to restrict a flow of the brake fluid from pump 8 to reservoir 160P. A check valve 6S is provided between reservoir 160S and pump 9, and arranged to allow a flow of the brake fluid from reservoir 160S to pump 9, and to restrict a flow of the brake fluid from pump 9 to reservoir 160S. Wheel cylinders W/C are connected, respectively, with passage reservoirs 160P and 160S by passages 14P and 14S. In passages 14P and 14S, there are provided solenoid-out-valves 5FL, 5RR, 5FR and 5RL each of which is a normally closed solenoid valve.

[Operation of Brake Apparatus] This brake apparatus 101 performs an anti-skid control (ABS control) to keep a slip rate of the wheel to a predetermined range, a vehicle behavior (movement) control to provide a yaw rate to the vehicle to stabilize the behavior (movement) of the vehicle, a brake assist control to boost in addition to the brake pedal operation of the driver, and an automatic brake control to produce a brake force based on the running condition irrespective of the intension of the driver. When the gear pump is actuated at the pressure decreasing control in the ABS control or at the pressure increase of the wheel cylinder, the brake fluid (the hydraulic fluid) flows from the wheel cylinder or the master cylinder to reservoirs 160P and 160S, and flows to low pressure chamber L1 which is on the pump suction side. Consequently, seal S5 (seal S6) is transformed (varies its shape) by the pressure on the pump discharge side, as mentioned above. The pressure of the wheel cylinder is acted through communicating groove 33 to high pressure chamber H1 in accordance with the transformation (deformation).

(1) The gear pump according to the embodiments of the present invention includes: a housing (2); a pump chamber (P1, P2) formed in the housing (2), the pump chamber (P1, P2) having a low pressure chamber (L1) and a high pressure chamber (H1); a gear (15, 18) disposed in the pump chamber (P1,P2), and arranged to be driven by a motor (M1) to perform a pump operation; a side plate (14, 22) disposed between a wall of the pump chamber (P1, P2) and the gear (15, 18), and arranged to seal a side surface of the gear (15, 18), the side plate (14, 22) including an annular receiving portion (14 j, 22 j) formed between the wall of the pump chamber (P1, P2) and the side plate (14, 22), the receiving portion having a bottom portion (30) and a side wall portion (31, 32); a seal member (S5, S6) disposed in the receiving portion (14 j, 22 j) of the side plate (14, 22), and arranged to liquid-tightly separate the low pressure chamber (L1) and the high pressure chamber (H1) of the pump chamber (P1, P2); a pressure introducing section (33) arranged to introduce a pressure generated by the pump operation, to a space between the bottom portion (30) of the receiving portion (14 j, 22 j) and the seal member (S5,S6), and thereby to separate the seal member (S5, S6) away from the bottom portion (30) of the receiving portion (14 j, 22 j. Accordingly, it is possible to decrease and optimize the variation (fluctuation) of the pressing forces of side plates 14 and 22 to gears 15 and 22 by the transformation or deformation of seals S5 and S6.

(2) In the gear pump according to the embodiments of the present invention, the seal member (S5, S6) is disposed with a clearance (34) between the seal member (S5, S6) the bottom portion (30) of the receiving portion (14 j, 22 j); and the pressure guide section (33) is arranged to introduce the pressure from the high pressure chamber (H1) to the clearance (34). There is formed, in advance, clearance 34. The pressure is introduced into clearance 34, and accordingly it is possible to improve the responsiveness to the introduction of the pressure.

(3) In the gear pump according to the embodiments of the present invention, the side wall portion (31) of the receiving portion (14 j, 22 j) includes a holding portion (35) arranged to abut on the seal member (S5, S6), and thereby to hold the seal member (S5, S6) in a predetermined position, and a plurality of the pressure introducing sections (33) provided alternatively in the holding portion (35) of the side wall portion (31) of the receiving portion (14 j, 22 j); and the pressure introducing section (33) has a width larger than a width of the holding portion (35) with respect to the bottom portion (30). Accordingly, it is possible to readily form the pressure guiding section (communicating groove 33) only by varying widths of receiving portions 14 j and 22 j.

(4) In the gear pump according to the embodiments of the present invention, the side plate (14, 22) is made from a resin; and the holding portion (35) and the pressure introducing section (33) are integrally formed. Accordingly, it is possible to readily mold holding portion 35 and the pressure guiding section (communicating groove 33).

(5) In the gear pump according to the embodiments of the present invention, the gear pump further comprises a center plate (7) fixed within the housing (2), and a pair of pump chambers (P1, P2) including the pump chamber; the pump chambers (P1, P2) are disposed on both sides of the center plate (7) to sandwich the center plate (7); the gear (16, 26) is disposed between the center plate (7) and the side plate (14, 22); the gear includes a drive gear (16, 26) arranged to rotate by the motor, and a driven gear (17, 27) arranged to be engaged with the drive gear (16, 26), and to be driven by the drive gear (16, 26); and the gear is a tandem external gear. Accordingly, the present invention can be applied to an external pump of the tandem type.

(6) A gear pump according to the embodiments of the present invention includes: a housing (2); a pump chamber (P1, P2) formed in the housing (2), the pump chamber (P1, P2) having a high pressure chamber (H1) and a low pressure chamber (L1); a gear (15, 23) disposed within the pump chamber (P1, P2), and arranged to rotate at least by a drive shaft (10); a side plate (14, 22) disposed adjacent to the gear (15, 23), between a side surface of the gear (15, 23) and a wall of the pump chamber (P1, P2), the side plate (14, 22) having an annular recessed groove (14 j, 22 j) formed in a surface confronting the wall (4 b, 6 d) of the pump chamber (P1, P2), and the annular recessed groove (14 j, 22 j) having a bottom portion (30); and a seal member (S5, S6) disposed in the annular recessed groove (14 j, 22 j) of the side plate (14, 22), and arranged to separate (partition) the high pressure chamber (H1) and the low pressure chamber (L1) of the pump chamber (P1, P2), and to be pushed in a direction away from the bottom portion (30) of the recessed groove (14 j, 22 j) by a pressure introduced from the high pressure chamber (H1) when the gear (15, 23) is driven. The thus-constructed gear pump can provide the same advantageous effects and operations as in (1).

(7) In the gear pump according to the embodiments of the present invention, the seal member (S5, S6) is disposed with a clearance (34) between the seal member (S5, S6) and the bottom portion (30) of the recessed groove (14 j, 22 j); and the high pressure chamber (H1) is arranged to introduce the pressure to the clearance (34). The thus-constructed gear pump can provide the same advantageous effects and operations as in (2).

(8) In the gear pump according to the embodiments of the present invention, the recessed groove (14 j, 22 j) of the side plate (14, 22) includes a side wall portion (31) disposed on the high pressure chamber's side; and the side wall portion (31) of the recessed groove (14 j, 22 j) includes a holding portion (35) arranged to abut on the seal member (S5, S6), and to hold the seal member (S5, S6) in a predetermined position, and a plurality of pressure introducing sections (33) provided alternatively in the holding portion (35); and each of the pressure guide sections (33) of the side wall portion (31) has a width larger than a width of the holding portion (35) with respect to the bottom portion (30) to introduce the pressure of the high pressure chamber (H1) to the clearance (34). The thus-constructed gear pump can provide the same advantageous effects and operations as in (3).

(9) In the gear pump according to the embodiments of the present invention, the side plate (14, 22) is made of a resin; and the recessed groove (14 j, 22 j), the holding portion (35), and the pressure introducing section (33) are integrally formed. The thus-constructed gear pump can provide the same advantageous effects and operations as in (4).

(10) In the gear pump according to the embodiments of the present invention, the gear pump further comprises a center plate (7) fixed within the housing (2), and a pair of pump chambers (P1, P2) including the pump chamber; the pump chambers (P1, P2) are disposed both sides of the center plate (7) to sandwich the center plate (7); the gear (15, 23) is disposed between the center plate (7) and the side plate (14, 22); and the gear (15, 23) includes a drive gear (16, 26) driven by the drive shaft (10), and a driven gear (17, 27) arranged to be engaged with the drive gear (16, 26), and to be driven by the drive gear (16, 26); and the gear pump is a tandem external gear. The thus-constructed gear pump can provide the same advantageous effects and operations as in (5).

(11) A gear pump according to the embodiments of the present invention includes: at least a pair of gears (16, 17) engaged with each other; a side plate (14, 22) disposed adjacent to the gears (16, 17), the side plate (14, 22) including an annular recessed groove (4 c, 6 d), and a shoulder portion; a housing (2) disposed at a position to sandwich the side plate (14, 22) with the gear (16, 17), and to confront the gear (16, 17); a seal member (S5, S6) disposed in the annular recessed groove (4 c, 6 d) of the side plate (14, 22), and arranged to seal a gap between the housing (2) and an end of the shoulder portion of the side plate (14, 22), and to separate a low pressure chamber (L1) and a high pressure chamber (H1) formed in a radial direction of the gear (16, 17); and a pressure introducing section (33) arranged to transform the seal member (S5, S6) by a pressure of the high pressure chamber in a direction toward the end of the shoulder portion. The thus-constructed gear pump can provide the same advantageous effects and operations as in (1).

(12) In the gear pump according to the embodiments of the present invention, the seal member (S5, S6) is disposed with a clearance (34) between the seal member (S5, S6) and the bottom portion (30) of the recessed portion (14 j, 22 j) of the side plate (14, 22); and the pressure introducing section (33) is arranged to introduce the pressure of the high pressure portion (H1) to the clearance (34). The thus-constructed gear pump can provide the same advantageous effects and operations as in (2).

(13) In the gear pump according to the embodiments of the present invention, the recessed portion (14 j, 22 j) of the side plate (14, 22) includes a side wall portion (31) on the high pressure chamber's side; the side wall portion (14, 22) of the recessed portion (14 j, 22 j) includes a holding portion (35) arranged to abut on the seal member (S5, S6), and to hold the seal member (S5, S6) in a predetermined position, and a plurality of the pressure guide sections (33) provided alternatively in the holding portion (35), and which has a width larger than the bottom portion (30) of the recessed portion (14 j, 22 j); the side plate (14, 22) is made of a resin; and the recessed groove (14 j, 22 j), the holding portion (35), the pressure introducing sections (33) are integrally formed. The thus-constructed gear pump can provide the same advantageous effects and operations as in (3) and (4).

(14) In the gear pump according to the embodiments of the present invention, the gear pump further comprises a center plate (7) fixed within the housing (2), and a pair of pump chambers (P1, P2); the pump chambers (P1, P2) are disposed on both sides of the center plate (7) to sandwich the center plate (7); the gear (15, 23) is disposed between the center plate (7) and the side plate (14, 22); the gear includes a drive gear (16,26) driven by the motor (M1), and a driven gear (17, 27) arranged to be engaged with the drive gear (16, 26), and to be driven by the drive gear (16, 26); and the gear is a tandem external gear. The thus-constructed gear pump can provide the same advantageous effects and operations as in (5).

Second Embodiment

Hereinafter, a gear pump according to a second embodiment of the present invention is illustrated. The following explanation is directed only to points different from the first embodiment, and repetitive explanation is omitted as to similar component parts to which the same reference numerals are given.

FIG. 21A is a view illustrating a state in which seal S5 is mounted. FIG. 21B is a view illustrating a state in which a low pressure is acted to seal S5. FIG. 21C is a view illustrating a state in which a high pressure is acted to seal S5. As shown in FIG. 21A, the gear pump according to the second embodiment includes a communicating groove 36 extending in a direction perpendicular to the axial direction of first side plate 14 (second side plate 22), in place of communicating groove 33, unlike the first embodiment. Communicating groove 36 includes a first end connected with high pressure chamber H1, and a second end connected with a part of clearance 34 near bottom portion 30. Accordingly, in the second embodiment, a contact area between seal S5 (seal S6) and high pressure side wall portion 31 is uniform around (over) the entire circumference. Accordingly, it is possible to prevent the concentration of the stress of seal S5 (seal S6), and to improve the durability. As shown in FIGS. 21A to 21C, the hydraulic fluid can be introduced through communicating groove 36 to cavity 34, like communicating groove 33 of the first embodiment. Therefore, it is possible to attain the same effect as the first embodiment. FIGS. 22A to 22C are views showing the gear pump according to the second embodiment when the high pressure side and the low pressure side are reversed. FIG. 22A is a view illustrating a state in which seal S5 is mounted. FIG. 22B is a view illustrating a state in which a low pressure is acted to seal S5. FIG. 22C is a view illustrating a state in which a high pressure is acted to seal S5. In addition, as shown in FIGS. 22A to 22C, even when the high pressure chamber H1 and low pressure chamber L1 is reversed at the ABS pressure decreasing control, the pressure is readily discharged, and it is possible to suppress the increase of the friction.

(15) In the gear pump according to the embodiments of the present invention, the gear pump further comprises a communicating groove (36) formed in the side plate (14, 22), and arranged to communicate the clearance (34) and the high pressure chamber (H1). Accordingly, it is possible to prevent the concentration of the stress to seals S5 and S6.

(16) In the gear pump according to the embodiments of the present invention, the gear pump is used for a brake apparatus for a vehicle; the brake apparatus includes a reservoir (160P, 160S) arranged to receive a brake fluid from a wheel cylinder (W/C) at an ABS pressure decreasing control; the gear pump is connected through the reservoir (160P, 1605) to the wheel cylinder (W/C) at the ABS pressure decreasing control, so that the pump chamber receives the pressure of the wheel cylinder; the pressure of the wheel cylinder (W/C) is acted to the low pressure chamber (L1); the seal member (S5, S6) is transformed by the pressure of the wheel cylinder (W/C) so that the pressure of the wheel cylinder (W/C) is acted through the communicating groove (36) to the high pressure chamber (H1) in accordance with the deformation. Accordingly, the pressure is readily discharged even when high pressure chamber H1 and low pressure chamber L1 is reversed at the ABS pressure decreasing control, the pressure is readily discharged, and it is possible to suppress the increase of the friction.

Third Embodiment

Hereinafter, a gear pump according to a third embodiment of the present invention is illustrated. The following explanation is directed only to points different from the first embodiment, and repetitive explanation is omitted as to similar component parts to which the same reference numerals are given.

The gear pump according to the first embodiment is the external gear pump of the tandem type. As shown in FIG. 23, the gear pump according to the third embodiment is the external gear pump of a single type, unlike the first embodiment. That is, component parts of second pump 9 of the first embodiment are omitted, and there is provided only the first gear pump 8. Moreover, in the third embodiment, seal member 7 and cover member 6 of the first embodiment are shortened in the forward and rearward directions, and integrally formed to form single seal member 7. Accordingly, it is possible to attain the same effects as the first embodiment.

Fourth Embodiment

Hereinafter, a gear pump according to a fourth embodiment is illustrated. The following explanation is directed only to points different from the first embodiment, and repetitive explanation is omitted as to similar component parts to which the same reference numerals are given.

FIG. 24 is a view illustrating a state in which seal S5 is mounted in the gear pump according to the fourth embodiment. As shown in FIG. 24, seal S5 (seal S6) includes a circular elastic transformation portion 37 made of an elastic material such as a rubber, and arranged to elastically transform (vary its shape), and a backup portion 38 made of a material having a rigidness larger than a rigidness of elastic transformation portion 37, and arranged to enforce (reinforce) elastic transformation portion 37. Elastic transformation portion 37 and backup portion 38 may be arbitrary fixed. Backup portion 38 has a substantially L-shaped cross section. Backup portion 38 is disposed to confront a boundary between high pressure chamber H1 and low pressure chamber L1. Elastic transformation portion 37 includes retaining portions 37 a which protrudes outwards, and each of which is located at a position corresponding to the end portion of L-shaped backup portion 38. Retaining portions 37 a are retained to backup portion 38, and accordingly it is possible to prevent the misalignment or deviation of elastic transformation portion 37. Accordingly, when the high pressure of the hydraulic fluid is acted, it is possible to prevent a transformed part of seal S5 from engaging in the interspace between first side plate 14 (second side plate 22) and recessed portion 4 c (recessed portion 5 d).

(17) In the gear pump according to the embodiments of the present invention, the seal member (S5, S6) includes an elastic transformation portion (37) arranged to elastically transform, and a backup portion (38) arranged to reinforce the elastic transformation portion (37); and the backup portion (38) of the seal member (S5,S6) confronts a boundary between the low pressure chamber (L1) and the high pressure chamber (H1). Accordingly, it is possible to prevent the engagement of the seal member (seals S5 and S6) when the pressure of the hydraulic fluid is acted.

Hereinafter, a gear pump according to a fifth embodiment of the present invention is illustrated. The following explanation is directed only to points different from the first embodiment, and repetitive explanation is omitted as to similar component parts to which the same reference numerals are given.

The gear pump 1 according to the first embodiment is the external gear pump of the tandem type. A gear pump according to the fifth embodiment is an internal gear pump of the tandem type, unlike the first embodiment. In particular, each of side plates 14 and 22 has a U-shaped cross section, as shown in FIG. 25. On the outer circumferences of side plates 14 and 22, there are formed, respectively, annular outer seal portions 40 and 41 each of which protrudes toward seal member 7, in place of seal blocks 14 e and 22 e. Outer seal portions 40 and 41 are fit, respectively, on the side seal portions 7 d of seal member 7. First gear 15 forming first pump 8 is disposed in a space surrounded by outer seal portion 40 of first side plate 14 and the corresponding side seal portion 7 d of seal member 7. Second gear 23 forming second pump 9 is disposed in a space surrounded by outer seal portion 41 of second side plate 22 and the corresponding side seal portion 7 d of seal member 7. Annular seals S8 and S9 are provided, respectively, on the outer circumference surfaces of outer seal portions 40 and 41, so as to secure the sealing separation between first and second pump chambers P1 and P2. Like holding members 21 and 24, parts of seals S8 and S9 are mounted, respectively, on side plates 14 and 22 to hold seal member 7 and side plates 14 and 22.

As shown in FIG. 26, first gear 15 of first pump 8 includes an outer rotor 42 having an internally toothed portion 42 a formed on an inner circumference surface of outer rotor 42, and an inner rotor 43 having an externally toothed portion 43 a formed on an outer circumference surface of inner rotor 43. Outer rotor 42 and inner rotor 43 are disposed in an eccentric state. Internally toothed portion 42 a of outer rotor 42 and externally toothed portion 43 a of inner rotor 43 are engaged with each other at an engagement portion 44 to form a pump chamber 45 surrounded by outer rotor 42 and inner rotor 43. Drive shaft 10 includes a drive raised portion 46 which is formed integrally with drive shaft 10, which is located at a position corresponding to the position of inner rotor 43 of each pumps 8 and 9, and which extends radially in a rectangular column from drive shaft 10. This drive raised portion 46 is engaged with recessed portion 43 b cut in the corresponding inner rotor 43. Drive raised portion 46 has an axial length smaller than an axial length (thickness) of inner rotor 43. Consequently, drive raised portion 46 is arranged to prevent the rotation of inner rotor 42 relative to drive shaft 10. Outer rotor 42 is arranged to rotate in the same direction as inner rotor 43 by the rotation of inner rotor 43. Outer rotor 42 rotates while outer rotor 42 slides on the inner circumference surface of outer seal portion 40. First side plate 14 includes through holes 47 and 48 located at positions to confront pump chamber 45. Each of through holes 47 and 48 may be formed into substantially crescent groove. Through hole 47 is connected through a space 29 formed between pump chamber 4 and first side plate 1, to a suction portion 50 of pump chamber 4. Through hole 48 is connected with discharge port 51 of pump chamber 4. On the other hand, second gear 23 of second pump 9 and second side plate 22 are formed like first gear 15 of first pump 8 and first side plate 14. Second side plate 22 includes two through holes 52 and 53. Through hole 52 is connected through a hydraulic passage 54 formed in cover member 6, to a suction port 55 of pump chamber 4. On the other hand, through hole 53 is connected through a space 56 formed between cover member 6 and second side plate 22, and through a hydraulic passage 57 formed in cover member 6, to a discharge port 58 of pump chamber 4.

As shown in FIG. 27, first side plate 14 includes an annular receiving portion 14 j formed on a rear surface of first side plate 14, like the first embodiment. Seal S5 is provided in receiving portion 14 j of first side plate 14. The discharge port 51 is the high pressure side. Receiving portion 14 j and seal S5 have the shapes which are opposite to the shapes in the inward and outward directions in the first embodiment. On the other hand, second side plate 22 includes an annular receiving portion 22 j formed on a front surface of second side plate 22, like the first embodiment. Seal S6 is provided in receiving portion 22 j of second side plate 22, as shown in FIG. 28.

[Operation of Gear Pump] Next, an operation of gear pump 1 according to the fifth embodiment is illustrated. In the thus-constructed gear pump 1, when drive shaft 10 is rotated by the motor in a clockwise direction of FIG. 26 shown by an arrow, outer rotors 42 of pumps 8 and 9 are driven through inner rotors 43. In this case, the pump operation (function) is acted by the variation of the volume of pump chambers 45 of gears 15 and 23. In first pump 8, the hydraulic fluid of the low pressure is introduced from suction port 50 through through hole 47 of firs side plate 14, and pressurized. Then, the hydraulic fluid is outputted through through hole 48 of first side plate 14 to discharge port 51. On the other hand, in second pump 9, the hydraulic fluid of the low pressure is introduced from suction port 55 through through hole 52 of side plate 22, and pressurized. Then, the hydraulic fluid is discharged through through hole 53 of second side plate 22 to discharge port 58. In this way, in gear pump 1 according to the fifth embodiment, both of pumps 8 and 9 can perform the suction operations and the discharge operations in the two separate hydraulic systems. Gear pump 1 serves as the internal gear pump of the tandem type.

The hydraulic fluid of high pressure chamber H1 is introduced in the rear surface of first side plate 14 from communicating groove 33 to clearance 34 at the low to high pressure operation of first pump 8, like the first embodiment. Accordingly, it is possible to attain the same effects as the first embodiment. On the other hand, the hydraulic pressure of high pressure chamber H1 is introduced in the front surface of second side plate 22 from communicating groove 33 to clearance 34 at the low to high pressure operation of second pump 9. Accordingly, it is possible to attain the same effects as the first embodiment.

Although the embodiments of the present invention has been described above, the invention is not limited to the embodiments described above. Various forms and modifications are included as long as they are not deviated from the gist of the invention. For example, when the drive shaft rotates in the direction opposite to the rotational direction of the drive shaft in the first embodiment, the hydraulic fluid flows from the discharge port to the suction port. Moreover, in the fifth embodiment, the gear pump may be an internal gear pump of a single type.

FIGS. 29A, 29B and 29C are enlarged sectional views showing a portion near a seal of a gear pump according to another embodiment of the present invention. FIG. 29A is a view illustrating a state in which seal S5 is mounted. FIG. 29B is a view illustrating a state in which a low pressure is acted to the seal. FIG. 29C is a view illustrating a state in which a high pressure is acted to the seal. In FIGS. 29A-29C, the same reference numerals are given to similar component parts. Moreover, the interspace between the first side plate and recessed portion 4 c may be not even. The first side plate 14 may have a stepped portion. In this case, communicating groove 33 may be formed into an annular shape so as to introduce the hydraulic fluid to clearance 34, irrespective of the pressure function of the hydraulic fluid.

The entire contents of Japanese Patent Application No. 2009-072938 filed Mar. 24, 2009 are incorporated herein by reference.

Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art in light of the above teachings. The scope of the invention is defined with reference to the following claims. 

1. A gear pump comprising: a housing; a pump chamber formed in the housing, the pump chamber having a low pressure chamber and a high pressure chamber; a gear disposed in the pump chamber, and arranged to be driven by a motor to perform a pump operation; a side plate disposed between a wall of the pump chamber and the gear, and arranged to seal a side surface of the gear, the side plate including an annular receiving portion formed between the wall of the pump chamber and the side plate, the receiving portion having a bottom portion and a side wall portion; a seal member disposed in the receiving portion of the side plate, and arranged to liquid-tightly separate the low pressure chamber and the high pressure chamber of the pump chamber; a pressure introducing section arranged to introduce a pressure generated by the pump operation, to a space between the bottom portion of the receiving portion and the seal member, and thereby to separate the seal member away from the bottom portion of the receiving portion.
 2. The gear pump as claimed in claim 1, wherein the seal member is disposed with a clearance between the seal member the bottom portion of the receiving portion; and the pressure guide section is arranged to introduce the pressure from the high pressure chamber to the clearance.
 3. The gear pump as claimed in claim 2, wherein the side wall portion of the receiving portion includes a holding portion arranged to abut on the seal member, and thereby to hold the seal member in a predetermined position, and a plurality of the pressure introducing sections provided alternatively in the holding portion of the side wall portion of the receiving portion; and the pressure introducing section has a width larger than a width of the holding portion with respect to the bottom portion.
 4. The gear pump as claimed in claim 3, wherein the side plate is made from a resin; and the holding portion and the pressure introducing section are integrally formed.
 5. The gear pump as claimed in claim 1, wherein the gear pump further comprises a center plate fixed within the housing, and a pair of pump chambers including the pump chamber; the pump chambers are disposed on both sides of the center plate to sandwich the center plate; the gear is disposed between the center plate and the side plate; the gear includes a drive gear arranged to rotate by the motor, and a driven gear arranged to be engaged with the drive gear, and to be driven by the drive gear; and the gear is a tandem external gear.
 6. The gear pump as claimed in claim 2, wherein the gear pump further comprises a communicating groove formed in the side plate, and arranged to communicate the clearance and the high pressure chamber.
 7. The gear pump as claimed in claim 6, wherein the gear pump is used for a brake apparatus for a vehicle; the brake apparatus includes a reservoir arranged to receive a brake fluid from a wheel cylinder at an ABS pressure decreasing control; the gear pump is connected through the reservoir to the wheel cylinder at the ABS pressure decreasing control, so that the pump chamber receives the pressure of the wheel cylinder; the pressure of the wheel cylinder is acted to the low pressure chamber; the seal member is transformed by the pressure of the wheel cylinder so that the pressure of the wheel cylinder is acted through the communicating groove to the high pressure chamber in accordance with the transformation.
 8. The gear pump as claimed in claim 2, wherein the seal member includes an elastic transformation portion arranged to elastically transform, and a backup portion arranged to reinforce the elastic transformation portion; and the backup portion of the seal member confronts a boundary between the low pressure chamber and the high pressure chamber.
 9. A gear pump comprising: a housing; a pump chamber formed in the housing, the pump chamber having a high pressure chamber and a low pressure chamber; a gear disposed within the pump chamber, and arranged to rotate at least by a drive shaft; a side plate disposed adjacent to the gear, between a side surface of the gear and a wall of the pump chamber, the side plate having an annular recessed groove formed in a surface confronting the wall of the pump chamber, and the annular recessed groove having a bottom portion; and a seal member disposed in the annular recessed groove of the side plate, and arranged to separate the high pressure chamber and the low pressure chamber of the pump chamber, and to be pushed in a direction away from the bottom portion of the recessed groove by a pressure introduced from the high pressure chamber when the gear is driven.
 10. The gear pump as claimed in claim 9, wherein the seal member is disposed with a clearance between the seal member and the bottom portion of the recessed groove; and the high pressure chamber is arranged to introduce the pressure to the clearance.
 11. The gear pump as claimed in claim 10, wherein the recessed groove of the side plate includes a side wall portion disposed on the high pressure chamber's side; and the side wall portion of the recessed groove includes a holding portion arranged to abut on the seal member, and to hold the seal member in a predetermined position, and a plurality of pressure introducing sections provided alternatively in the holding portion; and each of the pressure guide sections of the side wall portion has a width larger than a width of the holding portion with respect to the bottom portion to introduce the pressure of the high pressure chamber to the clearance.
 12. The gear pump as claimed in claim 11, wherein the side plate is made of a resin; and the recessed groove, the holding portion, and the pressure introducing section are integrally formed.
 13. The gear pump as claimed in claim 10, wherein the side plate includes a communicating groove connecting the clearance and the high pressure chamber.
 14. The gear pump as claimed in claim 10, wherein the seal member includes an elastic transformation portion arranged to elastically transform, and a backup portion arranged to reinforce the elastic transformation portion; and the backup portion confronts a boundary between the high pressure chamber and the low pressure chamber.
 15. The gear pump as claimed in claim 10, wherein the gear pump further comprises a center plate fixed within the housing, and a pair of pump chambers including the pump chamber; the pump chambers are disposed both sides of the center plate to sandwich the center plate; the gear is disposed between the center plate and the side plate; and the gear includes a drive gear driven by the drive shaft, and a driven gear arranged to be engaged with the drive gear, and to be driven by the drive gear; and the gear pump is a tandem external gear.
 16. A gear pump comprising: at least a pair of gears engaged with each other; a side plate disposed adjacent to the gears, the side plate including an annular recessed groove, and a shoulder portion; a housing disposed at a position to sandwich the side plate with the gear, and to confront the gear; a seal member disposed in the annular recessed groove of the side plate, and arranged to seal a gap between the housing and an end of the shoulder portion of the side plate, and to separate a low pressure chamber and a high pressure chamber formed in a radial direction of the gear; and a pressure introducing section arranged to transform the seal member by a pressure of the high pressure chamber in a direction toward the end of the shoulder portion.
 17. The gear pump as claimed in claim 16, wherein the seal member is disposed with a clearance between the seal member and the bottom portion of the recessed portion of the side plate; and the pressure introducing section is arranged to introduce the pressure of the high pressure portion to the clearance.
 18. The gear pump as claimed in claim 17, wherein the recessed portion of the side plate includes a side wall portion on the high pressure chamber's side; the side wall portion of the recessed portion includes a holding portion arranged to abut on the seal member, and to hold the seal member in a predetermined position, and a plurality of the pressure guide sections provided alternatively in the holding portion, and which has a width larger than the bottom portion of the recessed portion; the side plate is made of a resin; and the recessed groove, the holding portion, the pressure introducing sections are integrally formed.
 19. The gear pump as claimed in claim 16, wherein the gear pump further comprises a center plate fixed within the housing, and a pair of pump chambers; the pump chambers are disposed on both sides of the center plate to sandwich the center plate; the gear is disposed between the center plate and the side plate; the gear includes a drive gear driven by the motor, and a driven gear arranged to be engaged with the drive gear, and to be driven by the drive gear; and the gear is a tandem external gear.
 20. The gear pump as claimed in claim 17, wherein the side plate includes a communicating groove connecting the clearance and the high pressure chamber. 